OpenCV-3.4.3圖像通道處理

• 圖像通道處理

圖像讀取和處理都是按BGR通道順序進行的

 1 #include <iostream>
 2 #include <opencv2/opencv.hpp>
 3 #include "opencv2/highgui/highgui.hpp"
 4 #include "opencv2/imgproc/imgproc.hpp"
 5 
 6 int main(int argc, char **argv) {
 7     cv::Mat src = cv::imread("/home/cv/Downloads/images/P1180141.JPG", 1);
 8     cv::resize(src, src, cv::Size(src.cols / 3, src.rows / 3), cv::INTER_CUBIC);
 9     cv::imshow("original_after_resize", src);
10     
11     // blue channel
12     cv::Mat mytemp1(src.rows, src.cols, CV_8UC3, cv::Scalar(255, 0, 0));
13     cv::imshow("temp test", mytemp1);
14     // green channel
15     cv::Mat mytemp2(src.rows, src.cols, CV_8UC3, cv::Scalar(0, 255, 0));
16     cv::imshow("temp test", mytemp2);
17     // red channel
18     cv::Mat mytemp3(src.rows, src.cols, CV_8UC3, cv::Scalar(0, 0, 255));
19     cv::imshow("temp test", mytemp3);
20     cv::waitKey(0);
21     return 0;
22 }

或者使用mixChannels函數

 1 #include <opencv2/opencv.hpp>
 2 #include "opencv2/highgui/highgui.hpp"
 3 #include "opencv2/imgproc/imgproc.hpp"
 4 
 5 int main(int argc, char **argv) {
 6     cv::Mat src = cv::imread("/home/cv/Downloads/images/P1180141.JPG", 1);
 7     cv::resize(src, src, cv::Size(src.cols / 3, src.rows / 3), cv::INTER_CUBIC);
 8     for (int i = 0; i < 3; i++) {
 9         cv::Mat temp_bgr(src.rows, src.cols, CV_8UC3, cv::Scalar(0, 0, 0));
10         cv::Mat temp(src.rows, src.cols, CV_8UC1);
11         cv::Mat out[] = {temp_bgr};
12         int from_to[] = {i, i};
13         cv::mixChannels(&src, 1, out, 1, from_to, 1);
14         cv::imshow("single channel", temp_bgr);
15         cv::waitKey(0);
16     }
17 
18     return 0;
19 }

轉換到HSV顏色空間查看效果

 1 #include <iostream>
 2 #include <opencv2/opencv.hpp>
 3 #include "opencv2/highgui/highgui.hpp"
 4 #include "opencv2/imgproc/imgproc.hpp"
 5 
 6 int main(int argc, char **argv) {
 7     cv::Mat src = cv::imread("/home/cv/Downloads/images/P1180141.JPG", 1);
 8     cv::resize(src, src, cv::Size(src.cols / 3, src.rows / 3), cv::INTER_CUBIC);
 9     cv::imshow("original_after_resize", src);
10     
11     cv::Mat img_hsv;
12     cv::cvtColor(src, img_hsv, CV_BGR2HSV);
13     cv::Mat dst;
14     dst.create(img_hsv.size(), img_hsv.depth());
15 
16     int ch[] = {0, 0};
17     int ch1[] = {1, 0};
18     int ch2[] = {2, 0};
19 
20     // Hue 色調通道
21     cv::mixChannels(&img_hsv, 1, &dst, 1, ch, 1);
22     cv::imshow("hsv-h", dst);
23     // Saturation 飽和度通道
24     cv::mixChannels(&img_hsv, 1, &dst, 1, ch1, 1);
25     cv::imshow("hsv-s", dst);
26     // Lightness/Value 亮度/像素值通道
27     cv::mixChannels(&img_hsv, 1, &dst, 1, ch2, 1);
28     cv::imshow("hsv-v", dst);
29     cv::waitKey(0);
30 
31     return 0;
32 }

轉換到YUV空間或YCrCb空間查看效果

 1 #include <iostream>
 2 #include <vector>
 3 #include <opencv2/opencv.hpp>
 4 #include "opencv2/highgui/highgui.hpp"
 5 #include "opencv2/imgproc/imgproc.hpp"
 6  
 7 int main(int argc, char **argv) {
 8     cv::Mat src = cv::imread("/home/cv/Downloads/images/P1180141.JPG", 1);
 9     cv::resize(src, src, cv::Size(src.cols / 3, src.rows / 3), cv::INTER_CUBIC);
10     cv::imshow("original_after_resize", src);
11     
12     // YUV color space
13     cv::Mat img_yuv;
14     cv::cvtColor(src, img_yuv, CV_BGR2YUV);
15     cv::Mat dst;
16     dst.create(img_yuv.size(), img_yuv.depth());
17 
18     // Luminance, 明亮度，灰度值
19     int ch[] = {0, 0};
20     cv::mixChannels(&img_yuv, 1, &dst, 1, ch, 1);
21     cv::imshow("yuv-y", dst);
22     // Chrominance, 色彩及飽和度，指定像素的顏色
23     int ch1[] = {1, 0};
24     cv::mixChannels(&img_yuv, 1, &dst, 1, ch1, 1);
25     cv::imshow("yuv-u", dst);
26     int ch2[] = {2, 0};
27     cv::mixChannels(&img_yuv, 1, &dst, 1, ch2, 1);
28     cv::imshow("yuv-v", dst);
29 
30     // YCrCb color space
31     cv::Mat ycrb;
32     cv::cvtColor(src, ycrb, CV_BGR2YCrCb);
33     std::vector<cv::Mat> mv;
34     cv::split(ycrb, (std::vector<cv::Mat>&) mv);
35 
36     // Y channel
37     cv::Mat chy(src.rows, src.cols, CV_8UC1);
38     chy = mv[0].clone();
39     cv::imshow("Y", chy);
40     // Cr and Cb channel
41     // Cr反映RGB輸入信號紅色部分與RGB信號亮度值之間的差別
42     // Cb反應RGB輸入信號藍色部分與RGB信號亮度值之間的差別
43     cv::Mat chu(src.rows, src.cols, CV_8UC1);
44     chu = mv[1].clone();
45     cv::imshow("Cr", chu);
46     cv::Mat chv(src.rows, src.cols, CV_8UC1);
47     chv = mv[2].clone();
48     cv::imshow("Cb", chv);
49     cv::waitKey(0);
50 
51     return 0;
52 }

•  cv::Mat 類型的成員函數 depth 

查看官方文檔

inline
int Mat::depth() const
{
    return CV_MAT_DEPTH(flags);
}

其中的 CV_MAT_DEPTH 定義以下

#define CV_MAT_DEPTH(flags)     ((flags) & CV_MAT_DEPTH_MASK)

這裏的 CV_MAT_DEPTH_MASK 定義以下

#define CV_MAT_DEPTH_MASK       (CV_DEPTH_MAX - 1)

宏定義中的 CV_DEPTH_MAX 定義以下

#define CV_CN_SHIFT 3
#define CV_DEPTH_MAX (1 << CV_CN_SHIFT)

Mat::type
Returns the type of a matrix element.

C++: int Mat::type() const
The method returns a matrix element type. This is an identifier compatible with the CvMat type system, like CV_16SC3 or 16-bit signed 3-channel array, and so on.

表格來源(OpenCV學習十七：OpenCV中Mat的type)

出處暫不可考

Mat::depth
Returns the depth of a matrix element.

C++: int Mat::depth() const
The method returns the identifier of the matrix element depth (the type of each individual channel). For example, for a 16-bit signed element array, the method returns CV_16S . A complete list of matrix types contains the following values:

 

#define CV_8U 0
#define CV_8S 1
#define CV_16U 2
#define CV_16S 3
#define CV_32S 4
#define CV_32F 5
#define CV_64F 6
#define CV_USRTYPE1 7

 

CV_8U - 8-bit unsigned integers ( 0..255 )
CV_8S - 8-bit signed integers ( -128..127 )
CV_16U - 16-bit unsigned integers ( 0..65535 )
CV_16S - 16-bit signed integers ( -32768..32767 )
CV_32S - 32-bit signed integers ( -2147483648..2147483647 )
CV_32F - 32-bit floating-point numbers ( -FLT_MAX..FLT_MAX, INF, NAN )
CV_64F - 64-bit floating-point numbers ( -DBL_MAX..DBL_MAX, INF, NAN )

轉換函數

void cv::transform (InputArray src,
    OutputArray dst,
    InputArray m
)

The function cv::transform performs the matrix transformation of every element of the array src and stores the results in dst :

𝚍𝚜𝚝(I)=𝚖⋅𝚜𝚛𝚌(I)    (when m.cols=src.channels()), or

𝚍𝚜𝚝(I)=𝚖⋅[𝚜𝚛𝚌(I);1]    (when m.cols=src.channels()+1)

Every element of the N-channel array src is interpreted as N-element vector that is transformed using the MxN or Mx(N+1) matrix m to M-element vector - the corresponding element of the output array dst.

The function may be used for geometrical transformation of N-dimensional points, arbitrary linear color space transformation(such as various kinds of RGB to YUV transforms), shuffling the image channels, and so forth.

Parameters
    src    input array that must have as many channels(1 to 4) as m.cols or m.cols-1.
    dst    output array of the same size and depth as src; it has as many channels as m.rows.
    m    transformation 2x2 or 2x3 floating-point matrix.

• 以切片方式讀取cv::Mat

讀取矩陣中指定區域內的數據， OpenCV 有提供一種切片操做

template<typename _Tp> class Rect_
{
    public:
    typedef _Tp value_type;

    //! default constructor
    Rect_();
    Rect_(_Tp _x, _Tp _y, _Tp _width, _Tp _height);
    Rect_(const Rect_& r);
    Rect_(const Point_<_Tp>& org, const Size_<_Tp>& sz);
    Rect_(const Point_<_Tp>& pt1, const Point_<_Tp>& pt2);

    Rect_& operator = ( const Rect_& r );
    //! the top-left corner
    Point_<_Tp> tl() const;
    //! the bottom-right corner
    Point_<_Tp> br() const;

    //! size (width, height) of the rectangle
    Size_<_Tp> size() const;
    //! area (width*height) of the rectangle
    _Tp area() const;
    //! true if empty
    bool empty() const;

    //! conversion to another data type
    template<typename _Tp2> operator Rect_<_Tp2>() const;

    //! checks whether the rectangle contains the point
    bool contains(const Point_<_Tp>& pt) const;

    _Tp x; //!< x coordinate of the top-left corner
    _Tp y; //!< y coordinate of the top-left corner
    _Tp width; //!< width of the rectangle
    _Tp height; //!< height of the rectangle
};

typedef Rect_<int> Rect2i;
typedef Rect_<float> Rect2f;
typedef Rect_<double> Rect2d;
typedef Rect2i Rect;

cv::Rect

cv::Rect(int x, int y, int width, int height)

其中x和y分別表示所取區域的其實座標， width 和 height 分別表示所取區域的寬度和高度。例如

(cv::Mat(cv::Size(500, 500), CV_8UC1, cv::Scalar(0.0f)))(cv::Rect(0, 0, 100, 25))

就表示取原矩陣中以 (0, 0) 爲起點，寬100高25的區域。

• 保存圖片壓縮問題

http://www.javashuo.com/article/p-eklvnghx-kn.html

 

高斯金字塔操做

http://www.javashuo.com/article/p-tsbfztmn-dc.html

矩陣數據類型轉換操做

http://www.javashuo.com/article/p-apuwvdxy-dn.html

http://www.javashuo.com/article/p-zpklyiee-dx.html

取對數操做/歸一化操做等

https://blog.csdn.net/huayunhualuo/article/details/81486685

平滑操做

https://www.jianshu.com/p/6d203b0ffa11

圖像加減乘除

https://blog.csdn.net/qq_35294564/article/details/81058226

https://blog.csdn.net/qq_38784454/article/details/81514056

https://blog.csdn.net/u011177305/article/details/51264294

https://www.cnblogs.com/little-monkey/p/7202628.html

未完待續……